1366 - Incorrect integer value: '' for column 'customer_id' at row 1

insert into whos_online (customer_id, full_name, session_id, ip_address, time_entry, time_last_click, last_page_url) values ('', 'Guest', '166c5539e2e3b541449e87e237580f5e', '216.73.217.165', '1780980827', '1780980827', '/shop/product_info.php?info=p6_.html')

[XT SQL Error]